Robot control apparatus

ABSTRACT

The robot control apparatus according to the present invention is so adapted that, with regard to all kinds of motions commanded of a robot, the maximum velocity and time constant conforming to the type of robot motion can be designated for respective robot control axes (3) by a controller (1) which includes a selection table memory (4).

DESCRIPTION

1. Technical Field

This invention relates to a robot control apparatus which performsteaching/playback-type position control with regard to a robot having aplurality of drive axes.

2. Background Art

The basic operation in ordinary teaching/playbacktype robot controlcomprises a teaching operation, in which the robot is first movedmanually, by using a teaching pendant, to store motion point positioninformation and tasks to be performed at these points in the data memoryof a controller, an editing operation, in which the taught subjectedmatter stored in the data memory, namely the robot command data, isaltering using an MDI & CRT unit, etc., of the controller, and aplayback operation and automatic running performed after the teachingand editing operations.

In the playback operation and automatic running phase, a predeterminedvelocity command is applied to a drive mechanism of each controlled axisof the robot hand, thereby controlling the drive of these mechanismssimultaneously so that a predetermined task can be accomplished. Withregard to the traveling velocity of the robot arm at such time, motionvelocity can be decided as a ratio with respect to the maximum velocity,which is set for the robot arm, by an override function at the time ofmanual feed and by a motion velocity modification command and a setvalue of override at the time of playback operation. The reason for thisis that it is required that the traveling velocity of the hand besuitably altered, in dependence upon the task performed by the robot, atautomatic running and playback.

When teach data for each drive axis is decided in dependence upon theattitude of the robot arm with regard to taught starting and end pointsin the foregoing conventional robot control apparatus, there areoccasions where, depending upon the motion, the load acting upon a motorduring the motion exceeds the maximum output of a motor. Consequently,at the time of the teaching operation, it is required that a motionvelocity modification command be set in such a manner that the loadwhich will act upon the motor during the motion will fall within anallowable value range to lower the motion velocity. This places anexcessive burden upon the operator as far as performing the teachingoperation is concerned.

Conversely, depending upon the motion to be taught, there are times whenthe load acting upon the motor falls below the maximum output of themotor even though the robot arm moves at the set maximum velocity. Thereason for this is that in a conventional robot control apparatus, themaximum velocity of motion and the acceleration/deceleration timeconstant along each drive axis are fixed at constant values at all timesregardless of the type of robot motion performed.

More specifically, if a robot arm is capable of being driven at a highervelocity and, moreover, with a shorter time constant, whenevernecessary, the maximum velocity and time constant cannot be changed eventhough motion at the higher speed becomes possible. Consequently, theimprovement in robot efficiency is not satisfactory.

DISCLOSURE OF THE INVENTION

The present invention has been devised in order to solve the foregoingproblems and its object is to provide a robot control apparatus in whichthe maximum velocity and time constant of each axial motor are decidedfor each and every taught motion to simplify the teaching operation andraise the motion speeds.

In accordance with the present invention, there can be provided a robotcontrol apparatus for controlling a plurality of drive axessimultaneously by outputting a drive command to a motor having anacceleration/deceleration function, comprising memory means for storingteach data which stipulates a type of motion of a robot arm from astarting point to an end point, arithmetic means for deciding maximumvelocity and an acceleration/deceleration time constant along each driveaxis in such a manner that a load which will act upon each axial motorwill attain a maximum output of the respective motor during motionbetween taught points, and command means for forming, from the storedteach data, a drive command for each axial motor within the decidedmaximum velocity and having the respective acceleration/decelerationtime constant.

Accordingly, the robot control apparatus of the invention is such thatthe velocity and time constant of the motor for each axis are selectedbased on the attitudes of the robot at the taught starting point and endpoint, so that position can be controlled by forming control commands ofa robot, which has a plurality of drive axes, for higher velocity and ashorter time constant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the general construction of a robot controlapparatus according to the present invention, and FIG. 2 is a flowchartillustrating the flow for drive command computation performed by acontroller.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described in detailwith reference to the drawings.

The robot control apparatus shown in FIG. 1 is equipped with acontroller 1 and a teaching pendant 2. With regard to robot control axes3, a plurality of motors which read in drive commands viaacceleration/deceleration circuits of variable time-constant type arecontrolled by a controller 1.

The controller 1 comprises a data memory 4 for storing what is taught,namely robot command data, and a selection table memory 5 for storing avelocity and acceleration/deceleration time constant of each motor ofthe robot control axes 3, wherein velocity and time constant areselected based on the robot command data in the data memory 4.Registered beforehand in the selection table memory 5 upon taking intoconsideration motion conditions (movement attitude, external load, etc.)are a maximum value of velocity and an acceleration/deceleration timeconstant which will allow motor torque necessary for a motion to attainthe maximum output possessed by the motor.

FIG. 2 is a flowchart illustrating the flow for drive commandcomputation performed by the controller 1. When the teach data entersfrom the teaching pendant 2, the attitudes of the robot arm at startingand end points regarding each motion are given (step a), and maximumvelocity V₁ for each axis and a corresponding time constant T₁ are readout of the selection table memory 5 in conformity with the givenattitudes (step b). The robot arm is driven in accordance with themaximum velocity V and time constant T selected (step c).

It should be noted that, instead of using the selection table memory 5,an arrangement can be adopted in which computation formulae for velocityV_(i) and time constant T_(i) set by a coefficient conforming to motorload are stored in advance, and computations are performed successivelywith regard to the various axes based on the teach data from theteaching pendant 2.

Further, an arrangement is permissible in which plural sets of maximumvelocity V and time constant T are previously stored in the selectiontable memory 5 with respect to the same motion conditions, a maximumvelocity stipulating actual motion is computed from time constant dataread out at step b, and a different set of data is selected if thecomputed maximum velocity is less than a selected maximum velocity. Withsuch an expedient, it is possible to select a shorter time constant ifthe distance between the starting and end points is small.

Though an embodiment of the invention has been described, the inventionis not limited thereto but can be modified in various ways withoutdeparting from the scope of the claims.

Industrial Applicability

The present invention is capable of providing a robot control apparatusin which maximum velocity and acceleration/deceleration time constantare changed and set in such a manner that a load acting upon a motorduring a motion will attain the maximum output of the motor for each andevery motion between taught points, and drive of the robot arm iscapable of being controlled based on the set maximum velocity and timeconstant so that teaching efficiency and robot operating efficiency canbe improved.

We claim:
 1. A robot control apparatus for controlling a plurality ofdrive axes simultaneously by outputting a drive command to a motorhaving an acceleration/deceleration function, comprising:memory meansfor storing teach data which stipulates a type of motion of a robot armfrom a starting point to an end point; arithmetic means for decidingmaximum velocity and an acceleration/deceleration time constant alongeach drive axis in that a load which will act upon each axial motor willattain a maximum output of the respective motor during motion betweentaught points; and command means for forming, from said stored teachdata, a drive command for each axial motor within said decided maximumvelocity and having the respective acceleration/deceleration timeconstant.
 2. A robot control apparatus according to claim 1,characterized in that said arithmetic means decides a maximum velocityand an acceleration/deceleration time constant based on a selectionformula set for every axial motor.
 3. A robot control apparatusaccording to claim 1, characterized in that said arithmetic means has amemory for storing a selection table which decides a maximum velocityand an acceleration/deceleration time constant set for every axialmotor.
 4. A robot control apparatus according to claim 3, characterizedin that said memory has a plurality of selection tables for differentmaximum velocities, wherein if a maximum velocity at the time of amotion does not attain a set maximum velocity, said arithmetic meansdecides a maximum velocity by a different selection table.